1. The Field of the Invention
The present invention relates to methods and systems for attaching plunger rods to stoppers within pre-filled syringe barrels so as to ensure that the plunger rods are properly attached to the stoppers and to ensure that there has been no movement of the stoppers during the attachment that could potentially jeopardize the sterility of the liquid dosage housed within the syringe barrels.
2. The Relevant Technology
Clinical trials for some pharmaceutical drugs require that the drug dosage be delivered by injection through the use of a syringe. As part of the clinical trial protocols, the syringes are preloaded with a single dose of the drug or a placebo prior to shipping and use. As part of the preloading process, the plunger rod for each syringe is typically attached to a corresponding syringe stopper after the dosage and stopper have been placed within the syringe barrel. In this procedure, however, care must be taken so that no excessive movement of the stopper relative to the syringe barrel occurs while the plunger rod is being attached to the stopper. Excessive movement of the stopper relative to the syringe barrel can potentially result in contamination of the dosage.
In one approach to detecting whether the stopper has moved during the attachment of the plunger rod, a first digital image of the stopper is taken prior to attaching the plunger rod and a second digital image of the stopper is taken after the plunger rod is fully attached to the stopper. Information from the two digital images is compared to determine whether the stopper in the second digital image has moved relative to the stopper in the first digital image. If movement of the stopper is detected that is outside of a defined limit, the syringe and corresponding dosage are rejected and subsequently disposed of.
Although the above process is useful, it has some shortcomings. For example, the above process only detects movement of the stopper relative to its initial position and does not detect movement of the stopper relative to the syringe barrel. Thus, if the syringe barrel also moves between taking the first digital image and the second digital image, it is possible, depending upon the direction of movement and the length of movement, that the results deduced from the two digital images could either: 1) fail to detect when a stopper has moved beyond its defined limit relative to the syringe barrel, and should thus be rejected, or 2) determine that the stopper has moved beyond the defined limit and thus reject the syringe and dosage when in fact the stopper has not moved beyond the defined limit relative to the syringe barrel. Furthermore, conventional monitoring systems only determine if there has been movement of the stopper after the plunger rod has been fully attached. As such, the conventional systems do not account for movement of the stopper during attachment of the plunger rod where the stopper returns to its original position by the end of the attachment process. Other shortcomings also exist with current monitoring systems.
Accordingly, what is needed in the art are methods and systems that overcome all or some of the shortcomings of conventional monitoring systems.